On the Prediction of Unsteady Forces on Gas-Turbine Blades: Part 1 — Typical Results and Potential-Flow-Interaction Effects
This paper is a contribution to the study of the generation of unsteady forces on turbine blades due to potential-flow interaction and viscous-wake interaction from upstream blade rows. A computer program is used to compute the unsteady forces on a rotor. The accuracy of the computer program is tested by comparing the results of a steady-flow calculation case and of an unsteady-flow calculation case with theory and experiment respectively. Results are shown for typical stator-to-rotor-pitch ratios and stator outlet-flow angles. These results show that the first spatial harmonic of the unsteady force may decrease for higher stator-to-rotor-pitch ratios. This trend is explained by considering the mechanisms by which the unsteady forces are generated. In this paper the mechanism by which the potential-flow interaction affects the flow field to generate these unsteady forces is shown to vary with the stator-to-rotor-pitch ratio and with the outlet flow angle of the stator.